In situ chemical vapour co-deposition of Al and Si to form diffusion coatings on TZM

Multilayer alumino-silicide and silicide coatings were formed by in situ chemical vapour co-deposition of Al and Si on TZM (Mo-0.5Ti-0.1Zr-0.02C) alloy for improving its high-temperature oxidation resistance. MoSi2. and Mo (Si, Al)(2) layers were formed in the inner and the outer layers, respectively in the case of alumino-silicide coating. Whereas silicide coating consisted of Mo5Si3 and MoSi2 phases in the inner and the outer layers, respectively. 24-100-mu m thick coatings were formed by optimizing the pack Mixture of Al and or Si, NH4F and Al2O3 powders and conducting the experiments at 1000 degrees C for 8-36 h. MoSi2 layer showed a faster growth rate and presence of columnar grains. A small weight gain at the initial stages was observed during the oxidation tests of the coated samples under continuous or cyclic heating at 1300 degrees C in air. Neither cracks nor peeling of the coating layers were noticed after oxidation tests. (C) 2008 Elsevier B.V. All rights reserved.